Laser predrilling for high-precision positioning and installation of fully threaded screws in glued-laminated timber (glulam). Issue 2 (4th March 2023)

• Record Type: Journal Article
• Authors: Trautz, Martin; Grizmann, Denis; Pranjic, Andrija; Raupach, Michael; Glawe, Clarissa; Gillner, Arnold; Bornschlegel, Benedikt; Haasler, Dennis
• Is Part Of: Wood material science & engineering. Volume 18:Issue 2(2023)
• Page Start: 491
• Page End: 506
• Publication Date: 2023-03-04
• Subjects: Fully threaded screws -- wood processing -- laser -- predrilling -- pyrolytic ablation -- bond-behavior; Wood -- Periodicals; Wood products -- Periodicals; Building, Wooden -- Periodicals; 624.184
• DOI: 10.1080/17480272.2022.2051735
• Languages: English
• ISSNs: 1748-0272

Abstract

ABSTRACT: In many applications of joining and reinforcing timber elements with self-tapping fully threaded screws, the exact positioning of the screws becomes difficult as the screws tend to "stray" from their designated axis during insertion in wood and wooden semi-products. Experimental investigations show that besides natural local discontinuities like knots or resin inclusions, the screw-to-grain angle and the screws stiffness have an influence on the insertion process and thus can be identified as factors to a deviation of fully threaded screws. Mechanical predrilling cannot solve this problem, as the drills also stray during the predrilling process. As an alternative, a pyrolytic method of predrilling based on laser radiation proved suitable for obtaining guide holes with adequate straightness. This paper includes a description of the developed drilling processes using different lasers beam sources. The resulted borehole geometries of a QCW fiber laser, as well as an ultrashort pulsed laser, show satisfying results. Furthermore, the short- and long-term bond behavior of fully-threaded screws in a glued-laminated timber matrix, installed in laser predrilled guide holes, was tested and evaluated. The results show that with the new innovative wood processing method an exact positioning of fully-threaded screws is possible, almost without loss of withdrawal resistance of the screws.